Jiff missing methods

[jessekrubin]

This pull request includes several changes to the ryo3 project, primarily focusing on adding new functionality, refactoring existing code, and improving the structure of the codebase. The most important changes include adding new crate dependencies, updating the timespan function, and refactoring the JiffUnit and JiffRoundMode structures.

New functionality and dependencies:

• Added ryo3-macros crate to the project dependencies and updated Cargo.toml accordingly. [1] [2] [3]

Function updates:

• Updated the timespan function to include an unchecked parameter, allowing for unchecked timespan creation. Removed the redundant timespan_unchecked function. [1] [2] [3] [4]

Structural refactoring:

• Moved and refactored JiffUnit, JiffRoundMode, and other related structures from nujiff.rs to a new file jiff_types.rs. Updated all relevant imports and usages throughout the codebase. [1] [2] [3] [4] [5] [6] [7]

Code cleanup:

• Removed unused imports and redundant code from dev.rs and other files to improve code clarity and maintainability. [1] [2] [3] [4] [5] [6]

Documentation and changelog:

• Updated CHANGELOG.md to reflect the new changes, including the addition of new methods and placeholders for not-implemented features.